1. Field of the Invention
This invention relates to a resin composition for forming a thermistor body, and a thermistor.
2. Related Background of the Invention
Thermistors employing a material comprising a polymer layer and electrically conducting particles dispersed therein as a thermistor body, are generally known as organic thermistors or the like. Especially, thermistors having a PTC (positive temperature coefficient) wherein the resistance value increases sharply with temperature, are sometimes referred to as positive organic thermistors. These thermistors are used in devices such as overcurrent protection elements, heating protection elements, self-regulating heating elements and temperature sensors. These devices are required to have the characteristics that the room temperature resistance is sufficiently small, the change ratio of resistance value when the device is heated from room temperature to high temperature (change ratio of resistance value) is sufficiently large, and the variation of resistance value when the device is subjected to thermal histories such as heating and cooling (difference between the initial room temperature resistance value and room temperature resistance value after being subjected to thermal histories) is small. Hence, thermistors are required which can simultaneously satisfy these conditions to a high degree.
Conventionally, thermoplastic resins were widely used as the polymer layer forming the thermistor body of the thermistor. However, if a thermoplastic resin is used, cross-linking treatment or non-flammability treatment is required to increase heat resistance, and the manufacture of the thermistor body became complicated.
Thus, in order to facilitate manufacture with simple process, the use of a thermosetting resin as the polymer layer forming the thermistor body has been considered. For example, as a thermistor using a thermosetting resin composition, it has been proposed to disperse a fibrous electrically conducting substance in a thermosetting resin (e.g., U.S. Pat. No. 4,966,729), to disperse electrically conducting particles having spike-like projections in a thermosetting resin (e.g., Japanese Patent Publication No. 3101047) or disperse electrically conducting particles having spike-like projections and electrically conducting short fibers in a thermosetting resin (e.g., Japanese Patent Publication No. 3101048).